The intensive use of antibiotics has exerted a selective evolutionary pressure on micro-organisms to produce genetically based resistance mechanisms. Modern medicine and socio-economic behaviour exacerbates the problem of resistance development by creating slow growth situations for pathogenic microbes, e.g. in artificial joints, and by supporting long-term host reservoirs, e.g. in immuno-compromised patients.
In hospital settings, an increasing number of strains of Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus spp., and Pseudomonas aeruginosa, major sources of infections, are becoming multi-drug resistant and therefore difficult if not impossible to treat:                S. aureus is resistant to β-lactams, quinolones and now even to vancomycin;        S. pneumoniae is becoming resistant to penicillin or quinolone antibiotics and even to new macrolides;        Enteroccocci are quinolone and vancomycin resistant and β-lactam antibiotics are inefficacious against these strains;        Enterobacteriacea are cephalosporin and quinolone resistant;        P. aeruginosa are β-lactam and quinolone resistant.        
Furthermore, the incidence of multi-drug-resistant Gram negative strains such as Enterobacteriacea and Pseudomonas aeruginosa, is steadily increasing and new emerging organisms like Acinetobacter spp. and C. difficile, which have been selected during therapy with the currently used antibiotics, are becoming a real problem in hospital settings. Therefore, there is a high medical need for new antibacterial agents which overcome multidrug-resistant gram-negative bacilli such as A. baumannii, ESBL-producing E. coli and Klebsiella species and Pseudomonas aeruginosa (Clinical Infectious Diseases (2006); 42657-68).
In addition, microorganisms that are causing persistent infections are increasingly being recognized as causative agents or cofactors of severe chronic diseases like peptic ulcers or heart diseases.
WO 03/087098 discloses, among others, compounds of the general formula (A1)

wherein
one of Z1, Z2, Z3, Z4 and Z5 is N, one is CR1a and the remainder are CH, or one of Z1, Z2, Z3, Z4 and Z5 is CR1a and the remainder are CH;
R1 and R1a can notably be independently selected from hydrogen, halogen and C1-C6 alkoxy, provided that when Z1, Z2, Z3, Z4 and Z5 are CR1a or CH, then R1 is not hydrogen;
n is 0 or 1 and AB can notably represent a CR6R7—CR8R9 radical wherein each of R6, R7, R8 and R9 is independently selected from. H; (C1-6)alkoxy; (C1-6)alkylthio; halo; trifluoromethyl; azido; (C1-6)alkyl; (C2-6)alkenyl; (C1-6)alkoxycarbonyl; (C1-6)alkylcarbonyl; (C2-6)alkenyloxycarbonyl; (C2-6)alkenylcarbonyl; hydroxy, amino or aminocarbonyl which may be substituted; (C2-6)alkenylsulphonyl; or (C1-6)aminosulphonyl wherein the amino group is optionally substituted by (C1-6) alkyl or (C2-6)alkenyl; or R6 and R8 together represent a bond and R7 and R9 are as above defined;
R2 can be hydrogen, and
R4 can be a group —U—R52 in which R52 is an optionally substituted bicyclic carbocyclic or heterocyclic ring system (A)
containing up to four heteroatoms in each ring in which at least one of rings (a) and (b) is aromatic,
X1 is C or N when part of an aromatic ring or CR14 when part of a non aromatic ring;
X2 is N, NR13, O, S(O)x, CO or CR14 when part of an aromatic or non-aromatic ring or may in addition be CR14R15 when part of a non aromatic ring;
X3 and X5 are independently N or C;
Y1 is a 0 to 4 atom linker group each atom of which is independently selected from N, NR13, O, S(O)x, CO and CR14 when part of an aromatic or non-aromatic ring or may additionally be CR14R15 when part of a non aromatic ring,
Y2 is a 2 to 6 atom linker group, each atom of Y2 being independently selected from N, NR13, O, S(O)x, CO and CR14 when part of an aromatic or non-aromatic ring or may additionally be CR14R15 when part of a non aromatic ring;
each R13 can notably be hydrogen;
each of R14 and R15 can notably be hydrogen;
each x is independently 0, 1 or 2;
U is CO, SO2 or CH2; or
R4 can also be a group —X1a—X2a—X3a—X4a wherein the group X1a—X2a—X3a can notably be CH2CH═CH or COCH═CH and X4a can notably be a phenyl substituted one to three times wherein the substituents are notably selected from halogen atoms;
which compounds of formula (A1) can be used as antibacterials.
WO 2004/002992 discloses, among others, compounds of the general formula (A2)

wherein
both rings (x) and (y) can be aromatic,
Z1 can be a 3 atom linker group each atom of which can be independently selected from N and CH,
Z2 can be a 3 atom linker group each atom of which can be independently selected from N and CH,
Z3 can be CH,
Z4 and Z5 can both be carbon atoms,
n is 0 or 1 and AB represents notably a CR6R7—CR8R9 radical wherein each of R6, R7, R8 and R9 is independently selected from. H; (C1-6)alkoxy; (C1-6)alkylthio; halo; trifluoromethyl; azido; (C1-6)alkyl; (C2-6)alkenyl; (C1-6)alkoxycarbonyl; (C1-6)alkylcarbonyl; (C2-6)alkenyloxycarbonyl; (C2-6)alkenylcarbonyl; hydroxy, amino or aminocarbonyl which may be substituted; (C2-6)alkenylsulphonyl; or (C1-6)aminosulphonyl wherein the amino group is optionally substituted by (C1-6) alkyl or (C2-6)alkenyl; or R6 and
R8 together represent a bond and R7 and R9 are as above defined;
R2 can be hydrogen, and
R4 can be a group —U—R52 wherein U can be CH2 and R52 is an optionally substituted bicyclic carbocyclic or heterocyclic ring system (A)
containing up to four heteroatoms in each ring in which at least one of rings (a) and (b) is aromatic,
X1 is C or N when part of an aromatic ring or CR14 when part of a non aromatic ring;
X2 is N, NR13, O, S(O)x, CO or CR14 when part of an aromatic or non-aromatic ring or may in addition be CR14R15 when part of a non aromatic ring;
X2 is N, NR13, O, S(O)x, CO or CR14 when part of an aromatic or non-aromatic ring or may in addition be CR14R15 when part of a non aromatic ring;
Y1 is a 0 to 4 atom linker group each atom of which is independently selected from N, NR13, O, S(O)x, CO and CR14 when part of an aromatic or non-aromatic ring or may additionally be CR14R15 when part of a non aromatic ring,
Y2 is a 2 to 6 atom linker group, each atom of Y2 being independently selected from N, NR13, O, S(O)x, CO and CR14 when part of an aromatic or non-aromatic ring or may additionally be CR14R15 when part of a non aromatic ring;
each R13 can notably be hydrogen;
each of R14 and R15 can notably be hydrogen;
each x is independently 0, 1 or 2;
U is CO, SO2 or CH2;
R4 can also be a group —X1a—X2a—X3a—X4a wherein the group X1a—X2a—X3a can notably be CH2CH═CH or COCH═CH and X4a can notably be a phenyl substituted one to three times wherein the substituents are notably selected from halogen atoms;
which compounds of formula (A2) can be used as antibacterials.
WO 2004/035569 discloses antibacterial compounds of formula (A3)

wherein
R1 represents notably an alkoxy group;
each of X1, X2, X3, X4 and X5 independently represents nitrogen atom or a CR2 group;
R2 represents a hydrogen atom, a halogen atom, a hydroxy group, an alkyloxy group or a heteroalkyloxy group;
A represents notably an alkylene chain or a heteroalkylene chain;
R3 represents notably the group

wherein
n can be 0 (the group R4 being then absent), and
R5 can notably be a group of the formula —Y-Cy, Y being notably a C1-C6 heteroalkylene group and Cy being notably a possibly substituted phenyl or heteroaryl group;
whereby                an alkyl group may be straight or branched, comprise 1 to 20 carbon atoms and possibly include one or more halogen atoms in replacement of one or more of the hydrogen atoms of the alkyl group; and        a heteroalkyl group/a heteroalkylene chain stands for a straight or branched alkyl group/alkylene chain wherein one or more of the carbon atoms has/have been replaced by one or more heteroatoms which are each independently selected from inter alia an oxygen, a nitrogen and a sulphur atom;        by heteroaryl group shall be understood (notably) an aromatic group consisting of one or more rings and containing 5 to 14 ring atoms, one or more of these ring atoms being each independently selected from inter alia an oxygen, a nitrogen and a sulphur atom, which aromatic group can be unsubstituted or substituted by substituents which are each independently selected from inter alia halogen atoms, OH and NH2.        
It should however be noted that no specific example of compound of formula I as defined in this application is taught in WO 03/087098, WO 2004/002992 or WO 2004/035569.
It has now surprisingly been found that certain aminoethyl cyclohexyl derivatives are especially potent antimicrobial agents that are notably effective against a variety of both Gram positive and negative multi-drug resistant bacteria and especially against P. aeruginosa and Acinetobacter species.